Over a period of years synthetic sausage casings have been prepared from animal collagen which are particularly suited for the processing of pork sausages. As is known, sausage casings made from collagen are edible and they have the ability to transmit fat during the cooking of pork sausages and therefore have been found to be an acceptable substitute for natural casings.
In the manufacture of collagen casings a collagen source, typically hide collagen, is converted into a slurry containing from about 2 - 8% collagen by grinding the collagen source in a meat grinder and diluting with water. The collagen is acid swollen for releasing the collagen fibrils and destroying the identity of the individual fibers. The swollen collagen is extruded through an annular die to form a collagen tube. As the casing is extruded it is passed into a coagulating bath containing a dehydrating and deswelling agent, e.g., a concentrated solution of sodium sulfate or ammonium sulfate with a minor amount of alkali, e.g., sodium hydroxide to neutralize any free acid present in the casing. After the casing is coagulated, it is tanned suitably with an aluminum tanning agent for the purpose of providing sufficient strength to the casing to permit further processing. Often a second tanning operation is conducted using a dialdehyde as the tanning agent. The tanned casing is then washed, plasticized, and dried.